Ginkgo Biloba is the oldest genus among existing seed plants and the only survivor of the family Ginkgoaceae, that can be traced back more than 200 million years to the fossils of the Permian period. Preparations of Ginkgo Biloba leaves have been used as remedies in China for more than 5,000 years, I. e. since the earliest origin of Chinese herbal medicine. Phytopharmaceutical extracts from the leaves of Ginkgo biloba have been applied to treat cerebrovascular and peripheral vascular diseases in many countries, such as Germany, France, Japan and Korea since the 1960's.
The principal effective component in Ginkgo biloba leaves is flavonoids, that comprise at least 14 different compounds, such as flavonols, flavones, flavanols and biflavonoids etc. Among all these compounds, flavone glycosides and flavonol glycosides, that include kaempferol, quercetin and isorhamnetin with glucose or rhamnose, are the most emphasized in Ginkgo biloba extracts on the market for therapeutic purposes (Tebonin.RTM., Tanakan.RTM., Roekan.RTM., or "EGb 761"). As experiments have demonstrated, flavone glycosides and flavonol glycosides are potent antioxidants that scavenge oxygen free radicals, thereby preventing age-related cell and tissue damage that can adversely affect various mental functions, including memory and concentration; see J. Pincemail et al., La Presse Medicale Vol. 15 (1986), 1475-1479; J. Robak et al., Biochem Pharmacol Vol 37 (1988), 837-841 and J. Kleijnen and P. Knipschild, Ginkgo biloba (Drug Profiles), the Lancet 340:1136 (1992). In addition, the flavone glycosides and flavonol glycosides increase peripheral circulation. Methods of preparation of Ginkgo biloba extracts with a greatly enriched content of flavone glycosides as the active components are described in DE-B 17 67 098 and DE-B 21 17 429. These preparations are Ginkgo biloba monoextracts.
Besides flavonoids, another major active constituent in Ginkgo biloba leaves is terpene lactones, that include ginkgolides A, B, C, J, M and bilobalide. Ginkgolides are terpenoid substances with lactone structure; see K. Nakanishi, Pure and Applied Chemistry, Vol. 14 (1967), 89-113; M. Maruyama et al., Tetrahedron Letters (1967), 299-302 and 303-319 and K. Okabe et al., Ginkgolides, J. Chem. Soc. (1967), 2201-2206. They are twenty carbon cage molecules, incorporating a t-butyl group and six 5-membered rings A to F including a spiro [4.4] nonane, a tetrahydrofuran cycle and three lactone rings. The various ginkgolide structures differ only by the number and position of hydroxyl groups on the C1, C3 or C7 of the spirononane framework. Recently, it has been found that, by their property of inhibiting platelet activating factor (PAF), Ginkgolides A, B, C and M, especially ginkgolide B are effective in treating platelet activating factor acether-induced diseases such as asthma, bronchitis, dementia senilis, allergy, cardiac disorders, rheumatic diseases, etc. and a broad range of other circulatory system diseases; see U.S. Pat. No. 4,734,280; P. Braquet, Drug of the Future, 12, 643, 1987; V. Lamant et al., Biochem Pharmacol Vol. 36 (1987) 2749-52; K. Becker et al., Biomed Biochim Acta Vol. 47 (1988) 10-11; P. Braquet et al., J Ethnopharmacol Vol. 32 (1991) 135-9 and B. Steinke et al., Planta Med Vol. 59 (1993) 155-60. Ginkgolides A and B also have cerebroprotective property by increasing cerebral blood flow; see J. Krieglstein et al., European Journal of Pharmaceutical Sciences Vol. 3 (1995) 39-48. U.S. Pat. No. 5,002,965 describes a method of using ginkgolides to prevent reperfusion injury in organ transplantation.
DE-A 33 38 995 and the corresponding U.S. Pat. No. 4,571,407 disclose using bilobalide, a sesquiterpene lactone structurally related to ginkgolides (see K. Nakanishi et al., R. T. Major et al. and K. Weinges et al., J. Am. Chem. Soc., Vol. 93, 1971, 3544-3546) to treat encephalopathies, cerebral edemas, demyelinating neuropathies and myelopathies. When bilobalide was administered to the infarct area prior to occlusion to the middle cerebral artery, the cortical and infarct volume decreased substantially; see J. Krieglstein et al., European Journal of Pharmaceutical Sciences Vol. 3 (1995) 39-48. Experiments have also demonstrated that bilobalide can help restore the motor nerves in animals; see C. Bruno et al., Planta Med 59, 1993, 302-307. In addition, in vitro and in vivo tests have proved that bilobalide has the property to inhibit Pneumocystis carinii growth; see C. Atzori et al., Antimicrobe Agents Chemother 37(7), 1993, 1492-1496. U.S. Pat. No. 5,264,216 discloses a method of using bilobalide to treat an infection with a pathological strain selected from the group consisting of Trichomonas vaginalis, Staphylococcus aureus, Streptococcus faecalis, Escherichia coli, Lactobacillus sp. and Pneumocystis carinii. Activity of bilobalide against infection with Pneumocystis carinii has major utility in treating AIDS-associated infections.
In addition to the compounds mentioned above, Ginkgo biloba leaves also contain at least 12 alkyl phenolic acid compounds including ginkgolic acids (anacardic acids) that are 6-alkylsalicylic acids with n-C13- to n-C19-alkyl groups with 0 to 3 double bonds; see J. L. Gellermann et al., Phytochemistry, Vol. 15 (1976), 1959-1961 and Analytic. Chem., Vol. 40 (1968), 739-743. Structurally similar to the irritants in poison ivy, ginkgolic acids are the factors responsible for toxic effects of Ginkgo biloba extracts, that include gastrointestinal disturbances, headaches, skin irritation, dermatitis and edema. Many cases of allergic reactions after contact with Ginkgo biloba leaves or fruits have been reported since the 1960's; see G. A. Hill et al., J. Am. Chem. Soc., Vol. 56 (1934), 2736-2738; W. F. Sowers et al., Arch. Dermatol., Vol. 91 (1965), 452-456; L. E. Becker et al., J. Am. Med. Assoc., Vol. 231 (1975), 1162-1163; T. Nakamura, Contact Dermatitis, Vol. 12 (1985), 281-282; R. R. Tomb et al., Contact Dermatitis, Vol. 19 (1988) 281-3 and J. P. Lepoittevin et al., Arch Dermatol Res Vol. 281 (1989), 227-30. As a result, scientists in many countries have made notable efforts to develop substances and methods of desensitization against the allergies caused by ginkgolic acids (see U.S. Pat. No. 4,428,965). DE-B 17 67 098 and DE-B 21 17 429 developed a process to remove alkylphenol compounds with a chlorinated aliphatic hydrocarbons such as carbon tetrachloride. However the therapeutically valuable ginkgolides and the bilobalide are also considerably reduced in this process. DE-B 21 17 429 also adopted a technology to eliminate the polyphenol compounds with tanning properties (proanthocyanidins) in which lead compounds are applied. Problems with these processes are the health risks for the people involved, the potential danger to the environment and the possibility of undesirable residues in pharmaceutical.
Ginkgo biloba extract used most frequently at present for therapeutic purposes (Tebonin.RTM., Tanakan.RTM., Roekan.RTM., or "EGb 76111") contains 24% flavone glycosides and 6% terpene lactones; see K. Drieu, La Presse Medicale Vol. 15 (1986), 1455-1457. These are the ginkgolides A, B, C and J as well as the bilobalide, which makes up approximately half of the 6%. Ginkgo biloba extract normally contains less than 10 ppm (parts per million) alkylphenol compounds. The therapeutic daily dosage is 120 mg.
Great efforts have been made in the 1990's to enrich the active therapeutic components of Ginkgo biloba extract and to reduce its content of ginkgolic acids. At the same time, possibilities have been exploited to provide specific combinations of the effective components of Ginkgo biloba extract for different therapies. A combination of the ginkgolide components and the flavone glycosides will shift the active profile of the extract towards the anti-PAF-effects. By contrast, a combination of the bilobalide and the flavone glycosides will apply the active profile more effectively against encephalopathies, cerebral edemas, demyelinating neuropathies and myelopathies. At the same time, methods have been developed for not using chlorinated aliphatic hydrocarbons to remove the alkylphenol compounds and not using lead compounds to remove proanthocyanidins.
U.S. Pat. No. 5,399,348 refers to a method for preparation of Ginkgo biloba extract in which the alkylphenol compounds are separated not by using chlorinated aliphatic hydrocarbon, but first through a process of precipitation and filtration, then through a multi step liquid-liquid-extraction with an aliphatic hydrocarbon. However, a lead compound or a polyamide is used to remove proanthocyanidins. The method is described as follows: Ginkgo biloba leaves are extracted with an organic solvent selected from the group consisting of aqueous acetone, an aqueous alkanol having one to three carbon atoms and anhydrous methanol. Most of the organic solvent is separated from the extract to form an aqueous solution, which is then diluted with water to a solids content of 5 to 25 weight percent. The diluted aqueous solution is then cooled to precipitate and lipophilic components are removed. The aqueous solution is next treated with ammonium sulfate and extracted with methylethylketone, acetone, or a mixture of methylethylketone and acetone. The extract is diluted with water and alcohol to form an aqueous alcohol solution, which is treated with a lead compound or an insoluble polyamide. The treated aqueous alcohol solution is last extracted with an aliphatic or cycloaliphatic solvent to further remove the alkylphenol compounds and a dry extract is recovered.
In addition, after being extracted with a solvent selected from the group consisting of methylethylketone or a mixture of methylethylketone and acetone, the extract can be concentrated to a solids content of 50 to 70% and the concentrate is then diluted with water and ethanol to form an aqueous alcohol solution containing about 50 weight percent of water and about 50 weight percent of ethanol with a solids content of about 10 weight percent. Next an aqueous solution of a lead salt, that is selected from the group consisting of lead acetate, lead hydroxide acetate or lead nitrate, or an aqueous suspension of lead hydroxide, preferably a solution of lead hydroxide acetate, is added to the above-mentioned aqueous alcohol solution until a change in color from brown to umber takes place and precipitate is formed and separated. The aqueous alcohol solution is next extracted with an aliphatic or cycloaliphatic solvent to further remove the alkylphenol compounds and then concentrated to a maximum ethanol content of about 5%. Next ammonium sulfate is added up to a content of 20 weight percent. The aqueous alcohol solution obtained is extracted with a mixture of methylethylketone and ethanol in a ratio of 9:1 to 4:6, to form an organic phase extract, which is concentrated to a solids content of 50 to 70 weight percent. The resultant concentrate is dried. Instead of a lead salt, a polyamide such as polyamide-6, polyamide-6.6 or cross-linked polyvinyl pyrrolidone (Polyvidon) can also be used.
U.S. Pat. No. 5,399,348 discloses that by applying the above-mentioned methods, a preparation from the leaves of Ginkgo biloba can be achieved with a content of 20 to 30% flavone glycosides, 2.5-4.5% ginkgolides A, B, C and J, 2.0-4.0% bilobalide, less than 10 ppm alkylphenol compounds and less than 10% proanthocyanidins.
U.S. Pat. No. 5,322,688 develops a similar process to remove the alkylphenol compounds, which is described above. But instead of using a lead compound to remove proanthocyanidins, U.S. Pat. No. 5,322,688 adopts a process of extraction with a water-immiscible alkanol of 4 or 5 C-atoms such as n-butanol. The method is characterized in that Ginkgo biloba leaves are extracted with an organic solvent selected from the group consisting of aqueous acetone, an aqueous alkanol having one to three carbon atoms and anhydrous methanol. Most of the organic solvent is then separated from the extract by evaporation or distillation to form an aqueous solution, which is diluted with water to a solids content of 5 to 25 weight percent. The diluted aqueous solution is cooled to precipitate and remove the water-insoluble lipophilic components. Then the aqueous solution is treated with 10-30% ammonium sulfate and extracted with a solvent selected from the group consisting of methylethylketone and a mixture of methylethylketone and acetone. The extract is extracted next with butanol or pentanol and the butanol or pentanol extract is diluted with water and alcohol to form an aqueous alcohol solution, which is then extracted with an aliphatic or cycloaliphatic solvent to further remove the alkylphenol compounds. Finally the aqueous extract solution is concentrated and the resultant concentrate is dried to form a dry extract.
In addition, after being extracted with a solvent selected from the group consisting of methylethylketone and a mixture of methylethylketone and acetone, that is described above, the extract can also be concentrated to a solids content of 50 to 70% and then diluted with water to a solids content of about 10 weight percent. The aqueous concentrate is next extracted with water-immiscible C4 or C5 alkanol to form alkanol layers, that are concentrated to a solids content of 50 to 70 weight percent. The concentrate is then diluted with water and ethanol to form a solution having 5 to 20 weight percent dry extract in 20 to 60 weight percent aqueous ethanol, which is further extracted with an aliphatic or cycloaliphatic solvent to further remove alkylphenol compounds. Finally the aqueous extract solution is concentrated and the resultant concentrate is dried to form a dry extract.
U.S. Pat. No. 5,322,688 reveals that by applying the above-mentioned method, a preparation from the leaves of Ginkgo biloba can be achieved with a content containing 20 to 30 weight percent flavone glycosides, 2.5 to 4.5 weight percent of ginkgolides A, B, C and J, 2.0 to 4.0 weight percent bilobalide, less than 10 ppm alkylphenol compounds and less than 10 weight percent proanthocyanidins.
U.S. Pat. No. 5,389,370 also adopts the methods to remove the alkylphenol compounds and proanthocyanidins described by U.S. Pat. No. 5,322,688, but it provides a method to prepare a Ginkgo biloba extract with highly concentrated active components and their combinations. The process of U.S. Pat. No. 5,389,370 is characterized in that Ginkgo biloba leaves with at least 1.4% flavone glycosides are extracted with an organic solvent selected from the group consisting of aqueous acetone, an aqueous alkanol having up to 3 C-atoms and anhydrous methanol. Most of the organic solvent is then separated from the extract to a maximum content of 10% to form a concentrated aqueous solution, which is then diluted with water to a solids content of 15-20% by weight and left to cool until a precipitate forms. This precipitate, consisting of the lipophilic components which do not dissolve well in water, is filtered off. The remaining aqueous solution is then subjected to a multi step extraction with an ester of formic acid or acetic acid, such as ethyl acetate, or a mixture of ethyl acetate with an aliphatic or cycloaliphatic hydrocarbon. The dissolved ester is removed from the remaining aqueous solution by distillation and the resultant solution is extracted with a water-immiscible C-4 or C-5 alkanol. The alkanol phases are then washed with water, then subsequently concentrated and the residual quantities of the solvent are completely removed by azeotropic distillation. The residue is then diluted with 40 weight percent ethanol and water to form a diluted residue.
In addition, to remove accompanying substances of the extract obtained with the ethyl acetate or the ethyl acetate/hydrocarbon mixture in the above process, the extract can also be treated with activated carbon or by column chromatography using silica gel.
Furthermore, the extract obtained with the ethyl acetate or the ethyl acetate/hydrocarbon mixture in the above process can first be treated with activated carbon to remove accompanying substances. Thereafter the ginkgolides are crystallized. Pure bilobalide and remaining ginkgolides are then separated from the mother liquor by column chromatography.
The diluted residue obtained at the last step in the process mentioned above can be further extracted with an aliphatic or cycloaliphatic solvent in order to reduce the alkylphenol compounds. The water phase is then concentrated and evaporated to a dry extract.
U.S. Pat. No. 5,389,370 reports that by applying the above-mentioned method, a preparation from the leaves of Ginkgo biloba can be achieved with a content of 40 to 60% flavone glycosides; 5.5-8% ginkgolides A, B, C and J and 5-7% bilobalide, or 5.5-8% ginkgolides and less than 0.1% bilobalide, or 5-7% bilobalide and a maximum of 0.1% ginkgolides; 0-10% proanthocyanidins and a maximum of 10 ppm, preferably less than 1 ppm, alkylphenol compounds.
U.S. Pat. No. 5,637,302 concerns a method for preparation of Ginkgo biloba extract in which by subjecting the crude extract of Ginkgo biloba leaves to solvent extraction with a solvent comprising toluene and n-butanol, the use of chlorinated aliphatic hydrocarbon and a lead compound are avoided. In addition, by adopting this process, the problem of other inventions of using large volumes of different solvents which are miscible with one another is also resolved. The process of U.S. Pat. No. 5,637,302 is characterized in that Ginkgo biloba leaves are extracted with an aqueous solvent comprising a mixture of acetone and water or a mixture of methanol and/or ethanol and water. These partially aqueous extracts are then extracted directly with n-hexane or n-heptane or with a toluene/butanol mixture to remove inactive lipophilic substances such as alkylphenols and polyphenols. The defatted solution is concentrated next to a volume equal to the weight of the drug and then the concentrate is kept in a refrigerator for 24 hours and then centrifuged, that produces semi-crystalline precipitate comprising a mixture of dimeric flavonoids. The aqueous phase is extracted in countercurrent with a toluene/butanol mixture in which the volume ratio of toluene:butanol varies from 1:2 to 1:4. After counterwashing with water, the toluene-butanol phase is concentrated to a paste-like consistency and taken up with water or a water-alcohol mixture in order to remove the residual traces of toluene and butanol and dried.
In addition, the aqueous solution, which has been defatted and still contains a proportion of the dimeric flavones, can be passed over absorption resins such as an aromatic polymer that readily absorbs many active substances and has a marked activity for those of a phenolic nature. The absorbed active substances are then re-eluted from the resin with an organic solvent such as a lower (C1-4) alkanol or a water-miscible ketone.
U.S. Pat. No. 5,637,302 discloses that by applying the above-mentioned methods, a preparation from the leaves of Ginkgo biloba can be achieved with a content of 22 to 26% flavone glycosides, 2.5-4.5% ginkgolides, 2.5-4.5% bilobalide, substantially free of alkylphenol compounds and less than 10% proanthocyanidins.